More than 1 million people in the United States suffer a myocardial infarction (MI) each year. Myocardial infarction (MI) evokes an intense inflammatory response. Paracrine and autocrine released extracellular ATP (eATP), signaling through purinergic P2 receptors (P2X and P2Y), is a potent modulator of macrophage and fibroblast function. Extracellular ATP is hydrolyzed by the transmembrane protein Ectonucleoside triphosphate diphosphohydrolase 1 (CD39) to yield adenosine monophosphate (AMP), thereby halting pro-inflammatory ATP-mediated signaling. This goal of the project is to define the role of the macrophage and fibroblast- expressed CD39 on post-MI cardiac repair. To accomplish this goal we propose the following: Aim 1: To determine whether CD39 up-regulation is a protective mechanism that constrains autocrine ATP-driven inflammation, preventing exaggerated macrophage responses, and protecting from adverse post-MI fibrosis we will: 1) determine how CD39 activity impacts TLR-4-dependent and IL-4-dependent macrophage functions in vitro, 2) determine the impact of CD39 activity on the in vivo macrophage phenotypic transition from inflammatory to profibrotic functions during post-MI repair, and 3) Determine the role of macrophage CD39 on post-MI repair fibrosis in vivo. Aim 2: To dissect the purinergic pathways involved in CD39-mediated restraint of TGF-?1 activation of cardiac fibroblasts and determine the role of CD39 upregulation in modulating fibroblast function and regulating cardiac repair following MI we will 1) determine the downstream targets through which CD39 attenuates TGF-?1-mediated cardiac fibroblast inflammatory and fibrotic responses, 2) determine the impact of CD39 on the in vivo cardiac fibroblast phenotype during cardiac repair and 3) determine the impact of fibroblast CD39 on in vivo extracellular matrix remodeling during post-MI repair. Secondary Aim: To determine the impact of CD39 expression extracellular matrix remodeling we will use state-of-the-art MALDI-imaging mass spectroscopy to define the early and late biosignatures of cardiac ECM remodeling post-MI and determine the impact of CD39 on ECM remodeling. The outcomes of these studies will reveal the fundamental pathways by which CD39 regulates post-MI myocardial repair and could allow novel therapeutic approaches not only to treat fibrotic disorders of the heart, but also of the skin, lungs, bone marrow, liver, or kidneys, thereby providing an important translational impact.